Malaiyandi Latha M, Vergun Olga, Dineley Kirk E, Reynolds Ian J
Department of Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
J Neurochem. 2005 Jun;93(5):1242-50. doi: 10.1111/j.1471-4159.2005.03116.x.
Current evidence suggests that zinc kills neurons by disrupting energy production, specifically by inhibiting mitochondrial function. However it is unclear if the inhibitory effect requires zinc accumulation, and if so, precisely how zinc enters mitochondria. Here, using fluorescence microscopy to visualize individual rat brain mitochondria, we detected matrix zinc uptake using the fluorophore FluoZin-3. Fluorescence increased rapidly in mitochondria treated with micromolar free zinc, and was quickly returned to baseline by membrane permeant chelation. Zinc uptake occurred through the calcium uniporter, because depolarization or uniporter blockade reduced fluorescence changes. However, increased fluorescence under these conditions suggests that zinc can enter through a uniporter-independent pathway. Fluorescence steadily declined over time and was unaffected by acidification or phosphate depletion, suggesting that zinc precipitation is not a mechanism for reducing matrix zinc. Uniporter blockade with ruthenium red also did not change the rate of zinc loss. Instead, zinc appears to exit the matrix through a novel efflux pathway not yet identified. Interestingly, dye-loaded mitochondria showed no fluorescence increase after treatment with strong oxidants, arguing against oxidant-labile intra-mitochondrial zinc pools. This study is the first to directly demonstrate zinc accumulation in individual mitochondria and provides insight about mechanisms mediating mitochondrial zinc uptake and efflux.
目前的证据表明，锌通过破坏能量产生，特别是通过抑制线粒体功能来杀死神经元。然而，尚不清楚这种抑制作用是否需要锌的积累，如果需要，锌究竟是如何进入线粒体的。在这里，我们使用荧光显微镜观察单个大鼠脑线粒体，利用荧光团FluoZin-3检测线粒体基质对锌的摄取。在用微摩尔游离锌处理的线粒体中，荧光迅速增加，而通过膜通透性螯合剂可使其迅速恢复到基线水平。锌的摄取是通过钙单向转运体进行的，因为去极化或单向转运体阻断会减少荧光变化。然而，在这些条件下荧光增加表明锌可以通过不依赖单向转运体的途径进入。随着时间的推移，荧光稳定下降，并且不受酸化或磷酸盐耗竭的影响，这表明锌沉淀不是减少基质锌的机制。用钌红阻断单向转运体也不会改变锌流失的速率。相反，锌似乎通过一种尚未确定的新的外流途径离开基质。有趣的是，用强氧化剂处理后，加载染料的线粒体没有荧光增加，这与线粒体内对氧化剂不稳定的锌池的观点相悖。这项研究首次直接证明了锌在单个线粒体中的积累，并提供了关于介导线粒体锌摄取和外流机制的见解。
